The present invention relates to the field of seat belts which restrain passengers in vehicles, and, more particularly, relates to the field of safety alarm systems for use with automatic seat belts which are automatically deployed and draped around the bodies of people using vehicles.
Nowadays it is compulsory for passenger automobiles to be fitted with seat belts, which usually are of the "lap-and-diagonal" variety. However, because of human nature, often the rider in a vehicle neglects to fasten his seat belt, and accordingly is not protected in the event of an accident. Therefore, a requirement has arisen for a so-called "passive restraint" system, and particularly for such a system which uses seat belts. In such a system seat belts are automatically deployed and draped around the body of a person who sits in the vehicle, before the vehicle is driven. Usually, the seat belt moves out of the person's way as the person enters the vehicle and sits in the seat thereof, and then is tightened around his body, so as to function in the conventional way.
Usually the tightening of the belt associated with a particular seat of such a system is linked to the closing of the door through which access is made to that particular seat. A typical such system comprises a slider member which slides along a guide rail which is provided along the inner side of the roof of the vehicle, and to this slider member the upper end of the seat belt is fixed. The slider member is actuated and moved along the rail by a means such as a push-pull wire, whose motion is coupled to the door, and which pulls the slider member towards the front end of the rail when the door of the vehicle is opened, and pushes it to the rear end of the rail when the door is closed. By such a system, when a person opens the door so as to enter the vehicle, the upper end of the seat belt is moved forwards, allowing the person to enter the vehicle and to sit down without difficulty, and, when the person closes the door, the upper end of the seat belt is pulled backwards, so that the seat belt is tightened around the passenger. The lower end of the seat belt is typically coiled up in a conventional inertia reel belt retractor, so as to allow for automatic adjustment of the tension of the seat belt.
The pull on a seat belt during an accident is extremely high, and is quite beyond the capacity of any such push-pull wire to withstand. For this reason, when the door of the vehicle is closed, in preparation for starting the vehicle, and the slider member moves to the rear of the guide rail, a slide tongue provided on the slider member is arranged to lock into an anchoring buckle fitted to the vehicle body near the rear end of the guide rail, so that the motion of the slider member forwards along the guide rail is positively prevented, even if it is subjected to extreme forces during an accident. This anchor buckle is released when the push-pull wire is tightened, so as to pull the slider member forwards, when the door is again opened. Such a safety locking system is an essential part of such a passive restraint seat belt system as outlined above.
Further, such a passive restraint seat belt system must be equipped with an emergency release buckle, so that the person, held in his seat by the seat belt, can release himself in the event of an accident, or in the event of failure of the push-pull wire mechanism or the slide tongue/anchor buckle combination, or if he wishes to exit from the vehicle through a door other than the usual one, by clambering over the opposing seat, for example.
It is of the greatest importance that the proper engagement of such an emergency release buckle should be properly ensured, and also that the proper engagement of the above described slide tongue into the anchor buckle should be checked, as, in the event of either of these engagements being faulty, the person is no longer properly restrained in his seat, but is at severe risk in the case of an accident. Therefore, there has arisen a requirement for an automatic engagement checking system.